Installation problems exist at times where a need develops to retrofit a system connected gas detector, for example, a CO detector, into an existing alarm system. An installer may have to pull a multi-conductor cable from the installation point back to the control panel. This process can be both expensive and inconvenient.
It would be useful to be able to install gas detectors, or combination gas and fire detectors on an existing zone or loop with previously installed fire detectors without needing to pull additional wires.